Generally, the processing speed of a computer's central processing unit (CPU) has increased far more quickly than the access speed for a computer's hard disk drive (HDD). This speed gap between the CPU and the HDD contributes to application delay and can also increase power usage due to excessive spinning of the HDD. A hybrid drive is a computer hard drive configuration that addresses this speed gap. In a hybrid drive, non-volatile memory is used to supplement the spinning hard disk drive, in order to provide faster boot and resume by using faster memory, and to provide lower power consumption by keeping the HDD's spindle motor in idle mode more often. Such a hybrid drive configuration is particularly advantageous for battery operated computer systems, such as mobile computers or other mobile computing devices.
A simplified known hybrid drive configuration will be described. Referring to FIG. 1A which shows a known hybrid drive configuration 100, a non-volatile memory (NVM) cache 102 is added to be physically part of an HDD 104, to store frequently used sectors for fast boot and resume times. The HDD 104 with its on-board NVM cache 102 is placed on a system board, or motherboard, 106. Such an approach is typically supported by the computer's operating system.
Referring to FIG. 1B which shows another known hybrid drive configuration 110, an NVM cache 112 is provided directly on a computer's system board 114 and is in communication with an HDD 116 via the system board 114. If the entire operating system (O/S) is loaded in the NVM 112, booting can occur directly from the cache.
In each of the configurations in FIGS. 1A and 1B, a 128 MB minimum is currently recommended for the non-volatile memory cache. Non-volatile memory can be implemented in a hybrid HDD by way of an embedded flash disk, a one-chip solution using NAND flash memory die with existing HDD controllers, or a NAND flash memory die with a dedicated NAND controller.
U.S. Pat. No. 5,778,418 granted to Auclair et al. on Jul. 7, 1998 teaches the use of a common memory controller circuit to mediate access of the operating system to a combined mass storage system including a flash electrically erasable programmable read-only memory system and a rotating disk drive memory.
However these approaches cannot be used with existing computer hardware setups. The configuration in FIG. 1A requires a hard disk upgrade, where the new modified hard disk with NVM can have a unique form factor and require a unique interface. The configuration in FIG. 1B requires a system board upgrade, though a conventional HDD can be used. The approach in taught in U.S. Pat. No. 5,778,418 requires extra hardware in the form of a common memory controller circuit. In all of these approaches, the NVM memory is only dedicated for use as a non-volatile hard disk cache and is not easily replaced or upgraded.
Some operating systems permit creation of a “boot disk”. This is typically done on a removable medium for a spinning drive (floppy disk, CD or DVD), which can only hold a subset of the O/S booting portions for emergency purposes, and cannot hold the entire O/S. There is typically no space left on the removable medium for a spinning drive to act as a non-volatile cache for the hard disk drive. Moreover, since it is intended for use in a spinning drive, this boot disk approach does not solve the problem of decreased access speed and increased power consumption caused by spinning motors.